The Transport Secretary has been accused of putting politics ahead of passengers after a leaked letter showed he opposed the devolution of suburban rail services in the London area to keep the network "out of the clutches" of a Labour mayor.

Chris Grayling announced on Tuesday that he would not be handing control of routes currently operated by Southeastern to London Mayor Sadiq Khan despite the Government and then-mayor Boris Johnson publishing a joint prospectus in support of the measure in January.

The Evening Standard published a letter written in 2013 by Mr Grayling to Mr Johnson in which he said he was against the policy.

Mr Grayling, who was justice secretary at the time and was writing in his capacity as MP for Epsom and Ewell, wrote: "I would not be in favour of changing the current arrangements - not because I have any fears over the immediate future, but because I would like to keep suburban rail services out of the clutches of any future Labour mayor."

He also said he wanted MPs and local authorities outside of the Greater London boundary to maintain their "remit" over train services in their areas.

Explaining his decision not to devolve control of the lines run by Southeastern, Mr Grayling said the business plan presented by Labour mayor Sadiq Khan did not offer extra capacity and was simply based on "a belief that Transport for London (TfL) can run the system more effectively".

He added that he does want TfL to be "more closely involved" in the network with a representative on the franchise specification team.

But following the publication of the leaked letter, Bob Neill, Tory MP for Bromley and Chislehurst in south-east London, called for Mr Grayling to resign as Transport Secretary.

He told the Press Association: "If you look at what he said about the business case, that doesn't stand true to me.

"He took the decision which he had already taken beforehand on purely partisan grounds.

"I think it's disgraceful behaviour."

Mr Neill added: "He's done a great deal of harm to London commuters who would've benefited significantly.

"I think he should go."

Department for Transport figures show that more than a third of rail passengers have to stand on trains arriving in parts of London in the morning rush-hour.

Commuters on the Southern network have suffered months of delays and cancellations partly caused by strikes over changes to the role of conductors and high levels of staff sickness.

When plans to devolve suburban rail services were announced in January, then-transport secretary Patrick McLoughlin declared that the "new partnership" was an opportunity to "transform travel" and put passengers "at the heart of the rail network".

Mr Khan, who had hoped to take over responsibility for the South Eastern franchise when it is up for renewal in 2018, said: "The only proven way of improving services for passengers is giving control of suburban rail lines to TfL.

"This is why the Government and previous mayor published a joint prospectus earlier this year. There is cross-party support for this from MPs, assembly members, councils inside and out of London and businesses and their representatives.

"Anything short of this simply won't make the improvements desperately needed. It is a fact, TfL lines have more frequent trains, fewer delays and cancellations, more staff at stations and fares are frozen.

"We will keep pushing the Government to deliver the rail devolution they have promised and that is needed."

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